1. Field of the Invention
The present invention relates to an improved method for manufacturing a stator of a motor in which a plurality of coil pieces are sequentially inserted into a stator core.
2. Description of the Prior Art
A stator of a motor is generally formed by successively winding an enameled coil wire member 101 around a stator core 102 as shown in FIG. 1. A stator core 102 is made by laminating a plurality of ring steel plates 102 as shown in FIG. 2. On the inner circumference of the stator core 102, there are formed a plurality of slots 103 extending along the axis of the stator core 102. A coil wire member 101 is wound around the stator core 102 such that it passes through any of the slots 103, thereby forming a coil. Recently, motor stators have begun to be generally manufactured in a method different from the above. That is, a coil wire member 101 is wound beforehand around a die, or the like, a predetermined number of times to thereby form a coil shaped coil piece, and the coil piece is then inserted into one of the slots 103.
With electric current being transmitted through the coil wire member 101, a magnaflux is generated in the direction piercing the coil, driving the rotation of a rotor (not shown). Note that a part of a coil to be inserted into a slot 103 (a slot-inserted part) is referred to as a coil side 101a, while that connecting a pair of coil sides 101a is referred to as a coil end 101b.
In order to realize a high-output motor with a stator such as above, it has been desired to efficiently dispose coil wire members 101 in respective slots 103. For this purpose, a coil wire member having a rectangular cross section (i.e., a flat angular line), instead of a conventional circular cross section, has been proposed, so that adjacent coil wire members 101 can firmly contact each other on their flat sides. With this arrangement, a coil wire member 101 can be wound around a stator core 102 with less resulting space between adjacent windings. As a result, a tightly packed coil wire member can be highly efficiently disposed in slots 103. Moreover, in a method using a pre-formed coil piece, employment of an angular line to form a coil piece will attain the same effect.
However, a coil wire member having a rectangular cross section has higher rigidity than a coil wire member having a circular cross section. This resultantly gives wider curvature to coil ends, which thus project in the axial direction of the stator core. Worse, when coils are sequentially inserted into slots, straddling a predetermined number of slots as shown in FIG. 1, the equivalent number of coil ends to that of the straddled slots are overlapped to one another, significantly projecting in the diameter direction of the stator. This results in enlarging the size of a stator, and, by continuation, a motor using such a large stator.
Further, significantly projecting coil ends in the diameter direction of a stator core have adverse effects on the workability in assembling a coil. In addition, due to such large projection, the projected coil ends excessively contact an adjacent coil. This may bring about coating damage and resultant in insulation damage.